The present invention relates generally to polyolefin foams and, more particularly, to extruded foam sheets comprising ethylene/vinyl acetate copolymer.
Polyolefin foams, particularly polyethylene foams, and methods for manufacturing such foams are well known in the art. See, e.g., U.S. Pat. No. 5,348,984 (Lee), U.S. Pat. No. 5,462,974 (Lee), and U.S. Pat. No. 5,667,728 (Lee), the disclosures of which are incorporated herein by reference thereto. One of the most common polyethylenes used is low density polyethylene (LDPE).
While LDPE possesses a number of beneficial physical and chemical properties when used to produce a foamed sheet, a disadvantage of LDPE is that foams made therefrom generally have a lower surface coefficient of friction (COF) than would otherwise be desired for certain applications, including ‘blocking-and-bracing,’ load-bearing, and other protective packaging applications. LDPE foam is advantageously used in protective packaging applications due to its shock-absorbing characteristics, which allow the foam to absorb impacts that would otherwise be transmitted directly to the packaged object. When used for such purposes, the foam is placed in contact with the packaged object and positioned between the object and a shipping pallet or shipping crate on or in which the item is transported. In order to adequately protect the object, it is necessary to minimize relative movement between the object and the foam. Because of its relatively low COF, preventing or at least minimizing relative movement between LDPE foam the object protected thereby has proven to be difficult, generally requiring extra packaging materials and labor than would otherwise be required if the COF of the foam was higher.
A similar application wherein a higher COF would be desired is the use of LDPE foam for a tool box liner, i.e., a cushion upon which tools may be placed in a tool box to protect both the tools and the tool box, and also to decrease the noise generated when the tool box is moved or otherwise handled. Tool boxes often have individual drawers that are pulled out to provide access to a desired tool. Such movement places a lateral force on the tools at the point at which the tools rest on the surface of the base of the drawer. Absent sufficient frictional force between the tools and the drawer, the tools have a tendency to slide relative to the drawer surface towards the rear of the drawer, thereby accumulating in a disorderly jumble at the rear of the drawer. As can be appreciated, this situation makes it more difficult to locate the intended tool than if the tools were neatly arrayed on the base of the drawer. Similar tool movement can also occur during movement or other handling of the tool box.
Another property of LDPE foam that is undesirable for certain applications is its relative stiffness or hardness. This becomes a factor when the foam is used to make functional apparel, including floatation devices such as life jackets, or padding for sporting goods such as football, baseball, and hockey equipment. In such applications, a softer foam is desirable because a flotation device or piece of sporting equipment made from a softer foam is more comfortable to the person wearing the article than is a similar article made from a harder foam.
Accordingly, a need exists in the art for an improved foam that overcomes the foregoing disadvantages.